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Ref Clock input for PCIe

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Newbie
Posts: 2
Registered: ‎12-06-2017
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Ref Clock input for PCIe

For a x16 PCIe spanning Banks 220-223, can the PCIe ref clock be connected to either MGTREFCLK0 or MGTREFCLK1 of Bank 221?

 

Browsing through UG576, pg. 32, it looks like the clock source can be selected by CPLLREFCLKSEL[2:0]. 

 

Screen Shot 2017-12-06 at 10.45.12 PM.png

 

 


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Moderator
Posts: 5,501
Registered: ‎08-01-2008

Re: Ref Clock input for PCIe

[ Edited ]

As such no preference you need to make connection as per the UG576. I would recommend you to refer target board XDC file and see how it connected
https://www.xilinx.com/support/documentation/user_guides/ug576-ultrascale-gth-transceivers.pdf

 

check this board for reference 

https://www.xilinx.com/support/documentation/boards_and_kits/kcu105/ug917-kcu105-eval-bd.pdf

Thanks and Regards
Balkrishan
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Moderator
Posts: 5,501
Registered: ‎08-01-2008

Re: Ref Clock input for PCIe

[ Edited ]

Yes users can set  CPLLREFCLKSEL[2:0] to the corresponding values to select the source of the reference clock.You can find details of PCIE here
https://www.xilinx.com/support/answers/18329.html

 

I would recommend you to use single source however CPLLREFCLKSEL ports are used dynamically to select the reference clock source. After the selection has been made, the user design is responsible for resetting the CPLL and QPLLs via the active-High CPLLPD and QPLL0/1RESET ports, and the subsequent initialization process described in Reset and Initialization in the same user guide

Thanks and Regards
Balkrishan
--------------------------------------------------------------------------------------------
Please mark the post as an answer "Accept as solution" in case it helped resolve your query.
Give kudos in case a post in case it guided to the solution.
Newbie
Posts: 2
Registered: ‎12-06-2017

Re: Ref Clock input for PCIe

Thanks for the quick reply.

If a single clock is used, is there a preference to connect the ref clock to MGTREFCLK0 over MGTREFCLK1?

Moderator
Posts: 5,501
Registered: ‎08-01-2008

Re: Ref Clock input for PCIe

[ Edited ]

As such no preference you need to make connection as per the UG576. I would recommend you to refer target board XDC file and see how it connected
https://www.xilinx.com/support/documentation/user_guides/ug576-ultrascale-gth-transceivers.pdf

 

check this board for reference 

https://www.xilinx.com/support/documentation/boards_and_kits/kcu105/ug917-kcu105-eval-bd.pdf

Thanks and Regards
Balkrishan
--------------------------------------------------------------------------------------------
Please mark the post as an answer "Accept as solution" in case it helped resolve your query.
Give kudos in case a post in case it guided to the solution.